The invention relates to a device for ironing laundry comprising a water tank, a steam chamber, a soleplate provided with steam outlet ports, means for heating the soleplate and the steam chamber, a passageway between the water tank and the steam chamber for supplying cold water from the water tank to the steam chamber, a device for regulating the water flow through said passageway, a drip-stop valve arranged in said passageway, which valve opens above a certain temperature and closes below said temperature, said regulating device and said drip-stop valve being arranged in series in said passageway, and a bypass which bypasses the drip-stop valve and in which a valve is arranged for supplying a large amount of water directly to the steam chamber for cleaning the steam chamber, thereby bypassing the drip-stop valve.
Such a device is known from Philips' steam iron `Azur`, marketed since 1993. In this known ironing device the regulating device, which often is a metering valve, can be set by the user to obtain a certain water flow rate from the water tank to the steam chamber. In the steam chamber the water evaporates and the generated steam expels through the steam outlet ports in the soleplate, thereby improving the ironing performance. So, the metering or regulating device controls the steaming rate. In order to avoid having cold water enter the steam chamber while the temperature of the steam chamber is too low to generate steam, a so-called drip-stop valve is arranged in the passageway between the water tank and the steam chamber. This drip-stop valve is arranged in series with the metering valve. Opening and closing of the drip-stop valve depends upon the temperature of the steam chamber. If the temperature of the soleplate is too low to generate a sufficient amount of steam, the drip-stop valve is closed, so that no water can enter the steam chamber. If this temperature is high enough, the drip-stop valve opens. The amount of water dripping into the steam chamber depends upon the setting of the metering valve.
A problem with ironing devices is the proper cleaning of the steam chamber. It is well known that in hard water areas a layer of scale (generally calcium carbonate) will be built up on the inner surfaces of the steam chamber. Scale layers deteriorate the heat transfer to the steam chamber. Therefore, it is desirable for a user to have a possibility to remove the scale layer. Preferably, the ironing device should have a so-called self-clean function. For that purpose, the above described steam iron comprises a bypass which bypasses the drip-stop valve and in which a valve is arranged for supplying water directly to the steam chamber, thereby bypassing the drip-stop valve. With this construction it is possible for the user to open the self-clean valve to suddenly introduce a large amount of water into the steam chamber, thereby performing a self-clean action. The walls of the steam chamber are still hot, so that the large amount of cold water causes a kind of thermal shock effect on the walls, resulting in the layer of scale being cracked and breaking it into small particles which, subsequently, can be rinsed away through the steam outlet ports. This cleaning action can be repeated several times, whereby re-heating the steam chamber might be necessary, because introducing a large amount of cold water into the steam chamber causes a temperature drop of the wall of the steam chamber. In practice, it appears that scale is not removed properly from the walls, especially at the location where a thick layer of scale has been built up, i.e. where water enters the steam chamber for generating steam. The reason for this is that in the mentioned prior art steam iron water, for cleaning the steam chamber, has already been raised in temperature before it reaches said location of scale and is therefore less effective in cracking the layer of scale.